Bioequivalence and Bioavailability Forum

Dear Members,

Here i have a case study regarding Concentration availability of Zonisamide in human serum.

Considering, “Zonisamide extensively binds to erythrocytes, resulting in an eight-fold higher concentration of zonisamide in red blood cells than in plasma”.

As per regulatory guidance document, Zonisamide is to be measured in “Human Serum”.
As per regulatory guidance, during analytical phase of Zonisamide Suspension 20mg/mL quantitation, Zonisamide calibration standards and quality control samples are to be spiked in normal human serum.

During analytical method development and validation, it was observed that analyte peak area response ratio was found almost 5 times higher in serum samples as compared to blood samples.
Moreover, as Zonisamide is to be measured in serum, during evaluation of analyte stability in whole blood, Zonisamide QC samples to be spiked in whole blood and allowed to clot for approximately 30 minutes to get serum. As “Zonisamide extensively binds to erythrocytes, resulting in an eight-fold higher concentration of zonisamide in red blood cells than in plasma” there may be possibility to have lower concentration of Zonisamide in serum during subject sample analysis. Moreover, there may be possibility to not have exact Cmax data in human serum.

During clinical phase, after blood sample collection samples to be allowed to clot for approximately 30 min and QCs samples will not mimic this condition as they are to be spiked directly in Serum.

Is there any alternative practical approach possible to mimic scenario of subject sample collection during clinical phase and Qc samples spiking during analytical phase?????
Or can we change, matrix (i.e. from serum to blood) with valid justification?????

Thanks & regards,
Shreyas Goswami